1. On a cutting board, spread rosemary, garlic, pepper, and salt.
2. Trim off the fat from tri-tip roast.
3. Place roast on top of the seasoning. Press, and flip to coat it evenly on both sides. Repeat for other roast pieces.
4. With a plastic wrap, cover the roast, and pop it in refrigerator for 4 hours.
5. Preheat cooker to 210 degree F.
6. Place roast on grill of cooker, cover, and cook until the internal temperature reaches 143 degrees.
7. Take the roast out, and wrap it with foil and a towel. Allow it to rest for 45-60 minutes for juices to redistribute.
8. Thinly slice roast, and serve it with BBQ sauce.